The prevention of lowered image contrast and lowered visibility, that are caused by the reflection of external light from the sun or lighting equipment falling on a screen or by image reflection, is required of image display devices such as cathode-ray tube display devices (CRTs), plasma displays (PDPs), electroluminescent displays (ELDs) and liquid crystal displays (LCDs). Accordingly, it is common practice to provide an anti-specular reflection laminate on the outermost surface of an image display device from the viewpoint of reducing image reflection or reflectance using the principle of light scattering or the principle of optical interference.
As one of anti-specular reflection laminates, providing an anti-glare laminate on the surface of image display devices has hitherto been known as a method for regulating optical properties to realize excellent image displays. This method utilizes diffuse reflection of external light to decrease a specular reflection component, and has been mainly used for liquid crystal displays for personal computers. The anti-glare laminate is utilized for preventing a lowering in visibility as a result of specular reflection of external light or image reflection within image display devices. The anti-glare laminate is produced as having an anti-glare layer provided with various particles on a surface thereof, or as having an anti-glare layer having a concavo-convex shape formed by embossing (Patent Document 1).
On the other hand, display devices for TV sets (such as large screen liquid crystal displays and PDPs that are also used as TV sets, and especially large screen display devices for TV sets) are required to eliminate adverse affects caused by the reflection of external light or image reflection for improving visibility. Simultaneously, such devices are required to have excellent visibility in displaying highly entertaining images (e.g. movies and full-color images), such as high contrast and black color reproduction, especially wet glossy black color (glossy black feeling). Moreover, as for expression of black gradations in a bright room, especially in the low gradation region, it is required that the difference in black gradations is easily discernible and sensitivity is high. TV displays are often larger than personal computer displays and the installation position is commonly fixed to use, so that they are required to satisfy these properties regardless of the positions where they are fixed.
The purpose of conventional anti-glare laminates for personal computers is focused on providing appropriate visibility for office use, and such anti-glare laminates are excellent in the effect of reducing external light reflection or image reflection. However, when such anti-glare laminates are used on TV displays, black color reproduction including glossy black feeling in on-screen display, contrast and the like have sometimes been poor. Specifically, in the recognition of black and gray colors, such colors are sometimes recognized as a blurred, single-tone black color.
On the other hand, there is a growing demand for a higher level definition of panel resolution. The demand for a higher level definition of panel resolution can be satisfied by increasing the fineness of the concavo-convex shape of the anti-glare layer. However, when increasing the fineness of the concavo-convex shape of the anti-glare layer, it has often been pointed out that external light is reflected from the display surface resulting in such a phenomenon that, for example, the image display surface is seen white (whitening), or lowered contrast. Whitening of the image display surface leads to a decrease in color reproduction (particularly black color reproduction) or a decrease in contrast, both of which are problematic for TV displays that are required to show beautiful still images and movies.
In the case of using the anti-glare laminate on the liquid crystal image display surface of laptop computers and the like, when the light transmitted through the backside of backlight within a display is transmitted through the concavo-convex shaped surface of the anti-glare laminate formed on the outermost surface of the panel, the concavo-convex shape functions as fine lenses which disturb the displayed pixels and the like, that is, “glare” is likely to occur. This unfavorable phenomenon makes it difficult to attain the effect of the anti-glare laminate per se. In particular, the occurrence of the “glare” increases with increasing the definition of panel resolution, and it has thus been desired to effectively prevent this unfavorable phenomenon.
In order to eliminate this “glare”, for example, a method has been adopted in which surface concavoconvexes are densely and finely provided and, at the same time, scattering particles different in refractive index from the resin for forming the anti-glare layer are added to impart an internal scattering effect to the anti-glare laminate. Such methods could satisfactorily solve the problem of the “glare”, but on the other hand, they sometimes brought about surface whitening resulted from the increase in fineness of the concavoconvexes, or clouding caused by internal scattering effect or the like, resulting in a deterioration in black color reproduction and image contrast, and thus in lowered image visibility.
To the contrary, when an anti-glare layer is excluded to provide a smooth surface to an anti-specular reflection laminate, glossy black feeling can be reproduced; however, no reflection prevention can be achieved.
Accordingly, there is a high demand for developing an anti-specular reflection laminate that is capable of not only preventing the reflection of external light or images effectively but also achieving black color reproduction (especially glossy black feeling) and is particularly suitable for TV applications, in which displaying highly entertaining images is required and a constraint is imposed that the place to put a TV set is fixed and thus the degree of freedom in selecting the place is limited.
Further, a near-infrared ray (hereinafter abbreviated as NIR) emitted from the front surface of a plasma display at a wavelength from 800 to 1,100 nm can cause other devices such as a VTR to malfunction. Thus, to shield near-infrared rays, front filters are required to be imparted with an NIR absorbing function. Also, front filters may be required to have a function for shielding neon light, which is emitted from the front surface of a plasma display at a wavelength from 550 to 640 nm, or a function for shielding unnecessary various kinds of light, which are emitted from various kinds of displays at specific wavelengths.
Plasma display panels (hereinafter abbreviated as PDPs) use plasma discharge and produce unwanted electromagnetic waves in the frequency range from 30 MHz to 1 GHz. Thus, to prevent other devices (such as information-processing devices) from damage, a transparent electrical conductor sheet such as a conductive mesh sheet is normally provided on the front surface of a display as a front panel, in addition to the above functions, so as not to emit unwanted electromagnetic waves to the outside as much as possible.
In order to achieve the above-mentioned functions with as few layers as possible, it has been studied to use a plate-shaped composite filter as a front panel of a plasma display panel, in which an electromagnetic shielding sheet and optically functional layers such as a near-infrared absorbing layer, anti-specular reflection layer and anti-glare layer are stacked to shield unwanted electromagnetic waves emitted from an image display device and light at a specific wavelength and to impart various functions required of an image display device (Patent Document 2).    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-341070    Patent Document 2: JP-A No. 2002-311843